ORDBMS

Report
Object relational database
managmement systems (ORDBMS)
Adapted by Edel Sherratt from
originals by Nigel Hardy
ORDBMS
• Like a relational database management
system
• But with classes and inheritance
Basic Idea
• Extend the relational model
– do not throw away that strength
– recognise that OO has additional strengths
– add OO features to existing systems
Some examples
• Postgres
– Illustra, acquired by Informix, in turn acquired by
IBM
– PostgreSQL
• Omniscience, Omniscience corporation,
acquired by Oracle, became Oracle Lite
• DB2, Oracle database, Microsoft SQL Server
The Important extensions
1.
2.
3.
4.
•
structured types for attributes
references to tuples
methods
IDs for tuples
but relations (and queries on them) remain
central
Structured types for attributes
• As well as atomic types: int, float, char,
boolean . . .
• Also allow structs, sets, bags, lists, arrays .
• And more complex arrangements: bags of
structs
• i.e. relations
User defined types (UDTs) as attribute
types
• CREATE TYPE addrType AS
(street CHAR(50),city CHAR(20) );
• CREATE TYPE student AS
(name CHAR (30),sid char(9),
address addrType );
• CREATE TABLE company (name CHAR(20)
PRIMARY KEY,address addrType );
• keys are declared as part of tables - not UDTs
UDTs as table types
• CREATE TABLE students OF student;
• where student has three attributes
1. name
2. student_id
3. address
• and where address is a struct of
– street
– city
What about methods?
• include declaration in the type
• declare code separately
CREATE TYPE student AS ( ...
METHOD avgMark() RETURNS DECIMAL(5,2)
);
CREATE METHOD avgMark() RETURNS DECIMAL(5,2)
FOR student
BEGIN
...
END;
What about Identity
• Often hidden from user
• But can be made visible
• can be SYSTEM GENERATED
– like an OID
• can be DERIVED from the declared table key
And what about data manipulation?
• Essentially SQL, with programming language
extensions
• Some extras – for example to enable access to
object identifiers
Inheritance
• UDTs can “extend” UDTs
– all the attributes and methods of the parent
– plus any that are added
• tables can “extend” tables
– all the attributes, keys and constraints of the
parent
– plus any that are added
• Keywords vary
Querying inheritance structures
• by default, querying a parent searches all
subtypes
• the ONLY keyword limits it to the given table
• assume Staff is UNDER Person
SELECT p.name FROM Person p;
SELECT p.name FROM ONLY(Person) p;
SELECT s.name FROM Staff s;
BLOBs and CLOBs
•
•
•
•
Large OBjects
Binary and Character
stored and retrieved
cannot take part in standard search
comparisons
– though CLOB can be searched for substrings
• CLOBs for texts, code
• BLOBs for images, sounds, video
ORDBMS - conclusion
• here and growing
• builds on RDBMS expertise using other widely
available expertise
• introduces complexity and cost
• it does let us handle some of the difficult
applications much more easily
– but how common are they
– must the “traditional” applications pay the cost?

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